The present invention relates to data networking and more particularly to systems and methods for protecting against failure.
Hierarchical digital transmission standards such as SONET, SDH, and G.709 are commonly used in optical service provider networks. These standards define multiple layers of a transmission hierarchy where each layer represents transmission at a particular data rate. Multiple lower bandwidth transmission signals of one hierarchical layer can be multiplexed together to form a higher bandwidth transmission signal at a lower hierarchical layer. A higher hierarchical layer thus contains signals that are more finely granulated in bandwidth than a lower layer.
To provide high quality of service, networks employing such digital transmission standards require mechanisms to quickly respond to failures. To avoid disruption of data flow and preserve the user experience of voice and video services, it is desirable to reroute traffic affected by a link failure within 50 milliseconds. Numerous protection mechanisms have been developed in pursuit of this ideal.
Increasingly hierarchical digital transmission standard-based networks are being used to carry packet-based traffic such as IP traffic and also MPLS traffic. The hierarchical digital transmission standards can be said to operate at the optical layer (which includes the hierarchical transmission rate layers referred to above), whereas IP and MPLS are client layer protocols that exploit optical layer communication facilities. MPLS Traffic Engineering is an increasingly important technique for carrying traffic for which quality of service must be guaranteed. A set of techniques referred to as MPLS Fast Reroute has been developed to provide failure protection for MPLS Traffic Engineering tunnels. These protection mechanisms operate at the client layer whereas the protection mechanisms associated with the hierarchical digital transmission standards referred to above are associated with the optical layer.
Problems arise due to interactions between failure protection mechanisms operating at the different layers. It is desirable to inhibit the operation of optical layer protection mechanisms for traffic that is already protected at the client layer by a mechanism such as MPLS Fast Reroute. One way to accomplish this differential protection at the optical layer is to segregate protected traffic and unprotected traffic among different fibers or different wavelengths. This is extremely wasteful of transmission capacity.
Another prior art approach allows protected and unprotected traffic to share a link. When a failure occurs traffic is rerouted only for those paths that both employ the link and carry protected traffic. The traffic is rerouted at the endpoints of the path rather than at the point of failure. This approach requires the path restoration signaling to be done on a per-path basis between the points of failure and the path endpoints. Because there may be numerous protected paths with disparate endpoints, the signaling burden makes it difficult to achieve the objective of achieving rerouting of protected traffic within 50 milliseconds.
Yet another approach, limited to a ring topology, accomplishes its signaling at the link layer to reduce signaling traffic, but provides end-to-end restoration of protected paths. This approach relies on flooding signaling information around the ring and thus will not work in a mesh network where such flooding is impractical. Also, restoration is slowed somewhat by the need to signal failure all the way to the path endpoints.
What is needed are systems and methods for providing differential protection to traffic at the optical layer without incurring the drawbacks discussed above.